Inset plug-on with knockout retainer



FIG. 1 is a top plan view of an inset plug-on with knockout retainer, showing my design;

FIG. 2 is a front elevation view thereof, which is symmetrical with and identical to the left side, right side and rear elevation views; and,

FIG. 3 is a bottom plan view thereof. 

The ornamental design for an inset plug-on with knockout retainer, as shown and described. 